Its an integral part of the Sports Diver syllabus. Dive Leaders and Advanced Divers need to demonstrate experience of dives with mandatory deco before their qualification can be signed-off.
Rec Diving a Pony
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OK, now lets discuss whether "chips" means "potato chips" or "french fries"
diver00011
Registered
I don't think so. But his reasoning makes a lot of sense. Maybe we should all be doing this.
These days, any ocean dive of any depth is CCR (or doubles if I don't have cells, like right now!).
But if I was regularly doing relatively shallow dives in NYC area conditions and for whatever reason I didn't want to carry more than 100 CUF of gas with me, a small set of doubles would be a much better solution than a single tank and a pony bottle.
Cleaner setup, more stable, easier trim. If you have an LP hose blowout, or a primary or secondary reg failure with a single and pony, you have lost that gas (unless you want to try holding your breath and switching regs underwater, which isn't a great solution). With manifolded doubles you can just shut down that post. The only thing you lose is true 100% redundancy, so if you have a manifold failure that's a problem, but that's also extremely rare.
EFX
Contributor
Really? So, a simultaneous failure with a single and the pony at the same time is more likely than a manifold problem (or any of the failure points that can go wrong in a back doubles system)?!! And how does it differ from a simultaneous failure of both first stages on back doubles?
Why is switching regs even a consideration? Side-mount divers do it constantly for every dive. Most OW rec divers are trained to do it (for integral BC regs PADI advocates donating the primary with the donating diver going on the integral alternate).
Why is switching regs even a consideration? Side-mount divers do it constantly for every dive. Most OW rec divers are trained to do it (for integral BC regs PADI advocates donating the primary with the donating diver going on the integral alternate).
Not sure if I was clear.
We are comparing two systems for redundant gas supply - manifolded doubles vs. single tank and pony.
Blown LP hose or regulator failure are fairly common, certainly more than manifold failure. If either of those happens with a single tank and pony, you have lost access to the gas in the affected tank. The only way to access it would be to shut the valve and then switch regulators. I don't mean switch regulators like with sidemount diving. I mean removing a regulator from your working but empty tank and putting it on the full tank that had the failure, while holding your breath.
If the same thing happens on manifolded doubles, you can shut down the post with the affected regulator and breathe all of your gas in both tanks from your remaining working reg.
I may be misreading this but who dives a pony tank as a backup without a dedicated 1st and 2nd on it? It defeats the purpose of a pony to not have that in place the whole dive.
I think that you are misreading, or maybe I didn't explain it well enough. The question is the difference between two types of redundancy in case of gas source failure.
You are diving with a single AL80 on your back and a slung AL19 pony. Each tank has first and second stage regulators on it.
An LP hose blows on your AL80, or some other unfixable reg failure. Normally, this can drain a tank in a little over a minute, but let's say you are quick and reach behind you, and shut down your tank valve while deploying your pony. So even though you saved some gas in your AL80, now you have only 19 CUF of gas to breathe. The only way to access the gas in the AL80 would be to doff your rig, take the first stage off the AL80, breathe the pony down, and then while holding your breath take the first stage off the pony and attach it to the 80. You also would need to service both regs, but that's less important right now.
Now say you are diving manifolded doubles, and the same thing happens. You shut down the valve on the side of the failure, and breath from the reg on the other post. You still have access to your entire gas supply in both of your tanks.
You might say that you don't care about the extra gas, you have enough in the pony to get you to the surface. Fair enough, but it's always better to have more gas, for a slower and safer ascent. And since this is the advanced diving forum, it's also fair to consider the fact that you might want more gas if you have a deco obligation. While you could alternate your gear configuration depending on whether you were doing deco or not, it's nice to just have one configuration. Small manifolded doubles (which is what started this conversation) is a nice way of having good redundancy when you don't want to bring a big set of double tanks. That's all I'm saying. The manifold lets you get access to all of your gas in case of a reg failure. I have no major problem with single tank and pony, this is just an alternative with one advantage.
@doctormike gotcha understand now.
This thread has been a great read. My wife and I just picked up 2 AL40 with used apeks dst/at50's after our dive shop suggested it for lake Michigan wreck diving. Until reading this thread, I was under the impression we would just sling the al40 with 2nd stage kept on the bottle with rubber bands in addition to our long hose and necklace.
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